[en] Three methods for determing residual dichromate in COD evaluation were compared. The methods were: volumetric titration, potentiometric titration and spectrophotometric determination. The statistical analysis did not show any significance difference among the methods. For routine analysis, the spectrophotometric method is preferable to the other two because it is shorter, easier to carry out and produces smaller amounts of toxic wasted reactants

[en] Conventional power transformers are very simple and reliable electrical components and their efficiency, for large power rating, is well above 99 %. With such an excellent performance the improvement margin seems very limited. However, due to the large amount of power managed and the continuous service, also a small increase in the efficiency is desirable. As an example, consider that an efficiency increase of 0.5 % of a 25 MVA transformer may lead to savings in the order of 100 k euro/year. The use of superconducting materials opens the way to efficiency improvements on power transformers, and also adds important advantages such as size and weight reduction, that are very attractive for urban substations and transport applications. Moreover superconductors eliminate the need for refrigeration oil, thus avoiding the risk of fire hazard and reducing the environmental impact, in accordance with recent EU guidelines. In this paper a design procedure for HTS power transformers is reported. This procedure, that includes an analytical method for the calculation of the AC losses, is used to design a 25 MVA - 154 kV / 20 kV transformer based on commercial BSCCO tapes, and the evaluated performance are compared with those of a conventional copper transformer. The optimal working temperature is evaluated, and allowable cooling technologies are discussed. Considerations on the use of future 2nd generation YBCO coated conductors are also reported

[en] The article introduces the models and methodologies developed for sizing and for comparative analysis of impacts in life cycle assessment of innovative transformers size 25 MVA based on high critical temperature conductors

[en] Transformers in superconducting materials at high temperatures offer many advantages in economic, environmental and functional aspects, compared to traditional transformers. Are presented the potentials of superconducting transformers available, aspects of design and the international state of the art

[en] Ricerca sul Sistema Energetico S.p.A. (RSE) has been gaining a relevant experience in the simulation, design and installation of resistive-type Superconducting Fault Current Limiter (SFCL) devices for more than five years in the framework of a R and D national project funded by the Ricerca di Sistema (RdS). The most recent outcome of this research activity is the installation of a resistive-type BSCCO-based 9 kV / 3.4 MVA SFCL device in a single feeder branch of the Medium Voltage (MV) distribution network managed by A2A Reti Elettriche S.p.A (A2A) in the Milano area. This installation represents the first SFCL successfully installed in Italy. In this paper, we report on the main outcomes after a more than 1-year long steady-state field testing activity. The design of an upgraded device to be installed in the same substation has already been initiated: the new SFCL will allow to protect four different feeders, therefore implying a device upgrade up to 15.6 MVA.

[en] The physics of accretion disks is of fundamental importance for understanding of a wide variety of astrophysical sources that includes protostars, X-ray binaries, and active galactic nuclei. The interplay between hydrodynamic flows and magnetic fields and the potential for turbulence-producing instabilities is a topic of active research that would benefit from the support of dedicated experimental studies. Such efforts are in their infancy, but in an effort to push the enterprise forward we propose an experimental configuration which employs a modified cylindrical wire array Z-pinch to produce a rotating plasma flow relevant to accretion disks. We present three-dimensional resistive magnetohydrodynamic simulations which show how this approach can be implemented. In the simulations, a rotating plasma cylinder or ring is formed, with typical rotation velocity ∼30 km s^–1, Mach number ∼4, and Reynolds number in excess of 10⁷. The plasma is also differentially rotating. Implementation of different external magnetic field configurations is discussed. It is found that a modest uniform vertical field of 1 T can affect the dynamics of the system and could be used to study magnetic field entrainment and amplification through differential rotation. A dipolar field potentially relevant to the study of accretion columns is also considered.

[en] In the past, bismuth-based high temperature superconductors (HTS) was the only commercially available HTS conductors. The recent achievements in the production of MgB₂ tapes and YBCO coated conductors (CC) persuaded us to study both these HTS as potential candidates for Superconducting Fault Current Limiter (SFCL) applications. In this work, we report on critical current measurements on MgB₂ tapes and windings and YBCO CC at 4.2 K and in the temperature range 65-80 K, respectively. Results of electrical characterizations on MgB₂ and YBCO specimens having different metallic matrix, are used in a numerical model able to predict the SFCL behaviour in view of their potential applications

[en] In this paper the comparison of three different types of SFCL, the resistive, the inductive and the rectifier type, with reference to a significant position in the distribution network, is carried out. The design of the SFCL devices is developed and size, losses and refrigeration power are evaluated. An equivalent circuit model of each device is then derived and implemented, along with the scheme of the considered distribution network, in the EMTP program. The limiting effect, joule integral, recovery time and influence of SFCL devices on the healthy part of the system are studied and compared

[en] The problem of excessive short-circuit currents has become an important issue for power systems operators and there are clear indications for a growing interest in superconducting fault current limiter devices for MV and HV grids. In this work, we report on both simulation and electrical testing on single-phase SFCL prototypes developed in the framework of an Italian RTD project to be completed with a 3-phase SFCL unit by the end of 2005

[en] Modelling and design of superconducting fault current limiters (SFCL) requires accurate prediction of current-voltage behaviour and thermal response of HTS tapes carrying electrical current over I_c, since these characteristics affect the electrical behaviour of the SFCL during a fault. An experimental method was developed to measure current, voltage and surface temperature on short HTS tapes for electrical field values above I_c (1μV/cm), up to 10mV/cm. The measurements were performed under different thermal exchange conditions with current pulses having different duration and amplitude. The experimental results allowed to validate a numerical model for HTS tapes in overcurrent conditions